Trip systems are designed to respond to power faults detected in circuit breakers. Most simple trip systems employ an electromagnet to trip the circuit in response to short circuit or overload faults. The electromagnet provides a magnetic field in response to the current flowing through the breaker. When the current level increases beyond a predetermined threshold, the magnetic field "trips" a mechanism which causes a set of circuit breaker contacts to release, thereby "breaking" the circuit path.
Many simple trip systems also employ a slower responding bi-metallic strip, which is useful for detecting a more subtle overload fault. This is because the extent of the strip's deflection represents an accurate thermal history of the circuit breaker and, therefore, even slight current overloads. Generally, the heat generated by the current overload will cause the bi-metallic strip to deflect into the tripping mechanism to break the circuit path.
The tripping systems discussed above are generally adequate for many simple circuit breaker applications, but there has been an increasing demand for a more intelligent and flexible tripping system. For example, many industries today include three-phase power equipment that must be adjusted and monitored on a regular basis. Processor-based tripping systems have been developed to meet these needs.
To permit the tripping systems to be set for a selected current ratings and other tripping specifications, the systems have included jumper wires or other control mechanisms. In addition, to cover a wide range of selectable current ratings, the tripping systems have included complex calibration circuits having multiple calibration outputs. Moreover, the calibration circuits are relatively expensive because they include precision resistors for precise current measurements.